1. Field of the invention.
The present invention relates to ink jet cartridges used in ink jet printers and, more particularly, to the filling of ink jet cartridges with ink.
2. Description of the related art.
Ink jet printers utilize cartridges that hold ink and which selectively dispense or eject the ink during printing. The cartridges are filled with ink after manufacture. Once the cartridge is filled with ink, the cartridge is sealed and ready for use.
Ink jet cartridges typically include a body or housing defining a chamber or cavity for the ink, a printhead in fluid communication with the ink chamber including a plurality of ink emitting nozzles, and circuitry coupled to the printhead and adapted to allow controlled ejection of ink from selected nozzles during printing. The printhead/circuitry includes heating elements associated with each nozzle that allow the ink to be ejected from the nozzle by forming drops. Thus, the ink is naturally heated in a very small, localized manner during the printing process. Ink jet printing is essentially a thermal ink ejecting system.
However, historical data shows that ink jet printing with a temperature offset or at a rate of drop ejection that causes a temperature offset may cause individual nozzles to not fire. It has been found that the resulting elevation in printing temperature releases air entrained within the ink which inhibits the formation of the ink drop and thus the ejection of the ink drop from the nozzle. This is due to the fact that the ink was supersaturated with air during the process of filling the ink cartridge.
The amount of air that dissolves in ink is a function of the temperature of the ink. The function is an inverse ratio with cooler ink holding or entraining more air than warmer ink. Thus as the printhead heats up during use, air or gas is liberated from the ink in the form of small air bubbles. These air bubbles may clog the nozzles of the printhead.
Conventional filling processes for ink cartridges are accomplished with room temperature ink. As a result, the ink becomes supersaturated with air. This further results in visible air bubbles at the nozzles of the printhead even at the point of manufacture let alone during printing. Degassing the ink prior to filling the ink cartridge will not appreciably solve the problem as air quickly re-dissolves into the ink during the fill process.
What is needed is a method to reduce the supersaturation of the ink with air during the ink cartridge fill process.
What is also needed is a method of reducing the amount of entrained air in ink for ink jet cartridges.
What is further needed is an apparatus for reducing the amount of entrained air in ink for ink jet cartridges during the cartridge filling process.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for reducing the amount of air entrained in ink within ink jet printer cartridges.
In one form the present invention is a method for filling an ink jet cartridge with ink. The method includes providing ink suitable for ink jet printing, heating the ink to a temperature above ambient temperature to liberate air entrained in the ink and then filling the ink jet cartridge with the ink while substantially maintaining the elevated temperature of the ink.
The method preferably includes heating the ink with a temperature controlled resistance heater within a holding chamber baffled to allow the ink time to reach and maintain an appropriate temperature that is above ambient temperature. Resistance heated fill tubes in fluid communication with the holding chamber and the ink cartridge maintain the elevated temperature of the ink during filling of the ink cartridge. When the ink, now within the ink cartridge, reaches ambient temperature, it will be at or below an air saturation level of the ink for ambient conditions.
A target temperature for the ink is a temperature that is high enough such that the resulting supersaturation level for air in the ink is equivalent to the saturation level for air in ambient or room temperature ink. Once the ink cartridge is filled with the heated ink the ink cartridge is sealed. The ink is thereafter allowed to reach ambient temperature without further heating.
The method may also include utilizing an ultrasonic generator during heating to assist in the removal of air entrained in the ink. Prior to filling the ink cartridge and after heating the ink, the air evolved ink may also be stored in an accumulator/regulator tank. Such storage must be temporary as evaporation caused by the elevated temperature can change ink composition. Ink must then be re-heated prior to fill, or kept at reduced air pressure.
In another form, the present invention is an apparatus for filling an ink jet cartridge with ink. An ink holding tank is in fluid communication via a conduit with an air removal device adapted to elevate the temperature of the ink and liberate air entrained therein. The air removal device is in turn in fluid communication via a second conduit with an ink cartridge which is filled with the heated ink.
Preferably, the air removal device includes a temperature controlled resistance heater and a baffled ink holding chamber adapted to allow the ink time to reach and maintain a predetermined temperature. The second conduit may include a second resistance heater to help maintain the elevated temperature of the ink during transfer of the heated ink from the air removal device to the ink cartridge during filling.
An advantage of the present invention is that the ink within the ink cartridge will not form as many bubbles due to entrained air during printing.
Another advantage of the present invention is that agitation of the ink during the fill process does not result in excess entrained air.
Yet another advantage of the present invention is that clogs in ink jet cartridge printhead nozzles due to entrained air during printing are reduced.